Efficient Closed-Loop Schemes for MIMO WLAN

The existing wireless local area network (WLAN) systems defined by the IEEE 802.11a standard are single-input single-output (SISO) orthogonal frequency-division multiplexing (OFDM) based systems and can support data rates up to 54 Mbps. We consider deploying two transmit and two receive antennas in a WLAN system and double the maximum data rate to 108 Mbps. Applying our recent multiple-input multiple-output (MIMO) transceiver designs, including the geometric mean decomposition (GMD) and the uniform channel decomposition (UCD) schemes, we propose a simple and efficient closed-loop MIMO-OFDM design for much improved performance compared to its open-loop counterpart. The extra cost is to feed back unitary precoders, which can be made very moderate with careful precoder quantization.